I have 1520 components. When I go to my heavy weapons (can be any other) marine and unlock a module (sustained fire) for 800 components, the amount changes to 720 (correct). When I then go immediately to cards, I can still unlock the 2nd upgrade for 800 components as well, which results in -80 components.

come on guys, another bug? It seems this was rushed and not properly tested as those are so easily to be found.